Silver powder is used in the electronics industry for the manufacture of conductor thick film pastes. The thick film pastes are screen printed onto substrates forming conductive circuit patterns. These circuits are then dried and fired to volatilize the liquid organic vehicle and sinter the silver particles.
Printed circuit technology is requiring denser and more precise electronic circuits. To meet these requirements, the conductive lines have become narrower in width with smaller distances between lines. The silver powder particles necessary to form dense, closely packed, narrow lines must be as close as possible to monosized, dense packing spheres.
Many processes currently used to manufacture metal powders can be applied to the production of silver powders. For example, thermal decomposition processes, electrochemical processes, physical processes such as atomization or milling and chemical reduction processes can be used. Thermal decomposition processes tend to produce powders that are spongy, agglomerated, and very porous whereas electrochemical processes produce powders that are crystalline in shape and very large. Physical processes are generally used to make flaked materials or very large spherical particles. Chemical precipitation processes produce silver powders with a range of sizes and shapes.
Silver powders used in electronic applications are generally manufactured using chemical precipitation processes. Silver powder is produced by chemical reduction in which an aqueous solution of a soluble salt of silver is reacted with an appropriate reducing agent under conditions such that silver powder can be precipitated.
There is a need for a continuous process to efficiently produce silver particles and for a reactor in which to carry out the process.